Fuel compositions

ABSTRACT

Disclosed is a diesel fuel composition containing 2-ethylhexyl nitrate (2-EHN) and one or more organic peroxides for providing improved fuel economy. The organic peroxides may have a cyclic peroxide of the general formula (I).

The present application claims the benefit of European Procedure Patent No. 121950.4, filed Nov. 30, 2012.

FIELD OF THE INVENTION

The present invention relates to liquid fuel compositions having improved fuel economy benefits containing 2-ethylhexyl nitrate and one or more peroxides in a diesel fuel composition.

BACKGROUND OF THE INVENTION

Government regulations and market demands continue to emphasize conservation of fossil fuels in the transportation industry. There is increasing demand for more fuel-efficient vehicles in order to meet CO₂ emissions reductions targets. Any incremental improvement in fuel economy (FE) is of great importance in the automotive sector. There is therefore a continuing need for improvements in fuel economy performance of fuel compositions used to fuel an internal combustion engine.

The cetane number of a diesel fuel composition is a measure of its ease of ignition and combustion. With a lower cetane number fuel, a compression ignition (diesel) engine tends to be more difficult to start and may run more noisily when cold; conversely a fuel of higher cetane number tends to impart easier cold starting, to lower engine noise, to alleviate white smoke (“cold smoke”) caused by incomplete combustion.

There is a general preference, therefore, for a diesel fuel composition to have a high cetane number, a preference which has become stronger as emissions legislation grows increasingly stringent, and as such automotive diesel specifications generally stipulate a minimum cetane number. To this end, many diesel fuel compositions contain ignition improvers, also known as cetane boost additives or cetane (number) improvers/enhancers, to ensure compliance with such specifications and generally to improve the combustion characteristics of the fuel.

Organic nitrates have been known for some time as ignition accelerants in fuels, and some are also known to increase the cetane number of diesel fuels. Perhaps the most commonly used diesel fuel ignition improver is 2-ethylhexyl nitrate (2-EHN), which operates by shortening the ignition delay of a fuel to which it is added.

European consumption of 2-EHN grew from 75 kt/a to 101 kt/a from 2000 to 2008, and an average annual growth of approximately 3.5% has been predicted from 2008 to 2013.

The consumption of 2-EHN in North America (USA: 7.2 kt/a in 2008) is much lower than in Europe.

2-EHN is produced industrially by the nitration of 2-ethylhexanol, and in Europe this consumes almost a quarter of the production of this alcohol. The nitration of the alcohol involves reaction with a 1/1 mixture of undiluted nitric and sulfuric acids (using stoichiometric amounts of alcohol and nitric acid).

Organic peroxides have also been known for some time as cetane improvers.

US2011/0099979 discloses diesel fuel compositions and method for reducing NOx emissions. Paragraph [0038] of US2011/0099979 discloses cetane improvers which are organic compounds containing O—O bonds such as alkyl peroxides, aryl peroxides, alkyl aryl peroxides, acyl peroxides, peroxyesters, peroxyketones, per acids, hydroperoxides, and mixtures thereof. Examples include di-tert-butyl peroxide, cumyl peroxide, 2,5-dimethyl-2,5-di(tertiarybutylperoxy) hexane, tertiary butyl cumyl peroxide, benzoyl peroxide, tertiary butyl peracetate, 3,6,9-triethyl-3,9-trimethyl-1,4,7-triperoxononan, 2,2-di(tertiarybutyl)butane, peroxy acetic acid, tertiary butyl hydroperoxide. Di-tert-butyl peroxide is stated to be the preferred peroxide compound.

U.S. Pat. No. 4,045,188 discloses that the use of di-tert-butyl peroxide in conjunction with di-tert-butyl alcohol provides a synergistic effect in gasolines, particularly pronounced in leaded gasolines, to increase engine performance, measured by an increase in miles per gallon.

WO2004/072059 (EP1592682) relates to a composition comprising a cyclic ketone peroxide and one or more dialkyl peroxides.

WO99/32584 relates to a fuel comprising one or more cyclic ketone peroxides for reducing the emission of pollutants. Comparative Example D discloses a combination of 2-ethylhexyl nitrate and di-tert-butyl peroxide.

RU2010124844A relates to diesel fuel containing additives which increase cetane number. Additives consist of premixed cyclohexyl nitrate or 2-EHN and peroxides selected from di-tert-butyl peroxide, dicumyl peroxide and cumyl hydroperoxide. The effect of these additives is high cetane number of diesel fuel and low content of nitrogen oxides in exhaust gas.

“Unique trifurcated hydrogen bonding in a pseudopolymorph of tricyclohexane triperoxide (TCTP) and its thermal studies”, Chiranjeev Sharma Neupane, Satich Kumar Awasthi, Tetrahedron Letters, accepted manuscript 28 Aug. 2012, discloses that cyclic peroxides have been studied as cetane enhancers. This document discloses the synthesis of TCTP (tricyclohexane triperoxide).

“Synthesis and cetane-improving performance of 1,2,4,5-tetraoxane and 1,2,4,5,7,8-hexaoxonane derivatives”, Ambadas B Rode, Keunwoo Chung, Young-Wun Kim, In Seok Hong, Energy & Fuels, 2010, 24, pages 1366 to 1639, discloses examples of diesel fuels containing a combination of 2-EHN with cyclic ketone peroxide compounds 3a (tetraoxane), 4b, 4c and 4d (hexaoxonanes).

“Solid deposits from thermal stressing of n-dodecane and Chinese RP-3 jet fuel in the presence of several initiators”, Guozhu Liu, Yongjin Han, Li Wang, Xiangwen Zhang, Zhentao Mi, Energy & Fuels, 2009, 23, pages 356 to 365, discloses 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxononane (TEMPO) and demonstrates the role of initiators in the carbon deposition because of thermal cracking of jet fuel.

“Supercritical thermal cracking of N-dodecane in the presence of several initiator additives: Products distribution and kinetics”, Guozhu Liu, Yongjin Han, Li Wang, Xiangwen Zhang, Zhentao Mi, Energy & Fuels, 2008, 22, pages 3960 to 3969, discloses 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxononane (TEMPO) and demonstrates thermal cracking of n-dodecane in the presence TEMPO.

SUMMARY OF THE INVENTION

It has now been found that 2-EHN together with organic peroxides can improve the fuel economy properties in a diesel fuel composition.

Accordingly, in one embodiment, a diesel fuel composition is provided comprising a diesel base fuel, 2-ethylhexylnitrate and one or more peroxides selected from the group of peroxides represented by the general formula (I) below:

wherein R1, R3, and R5 are independently selected from the group consisting of hydrogen, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties; R2, R4 and R6 are independently selected from the group consisting of hydrogen, C2-C20 alkyl, C3-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties; and each of R1 to R6 may optionally be substituted with one or more groups selected from hydroxyl, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido.

In another embodiment, a method of operating an internal combustion engine and/or a vehicle powered by such an engine is provided, which comprises introducing into a combustion chamber of the engine the diesel fuel composition and operating the internal combustion engine and/or vehicle powered by such an engine.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the Derived Cetane Number (DCN) of the fuel blends tested in Example 2.

DETAILED DESCRIPTION OF THE INVENTION

In order to assist with the understanding of the invention several terms are defined herein.

The term “fuel economy” as used herein refers to optimized efficiency of an engine consuming fuel, i.e. the same power output can be obtained from the engine while consuming less fuel (and therefore emitting less carbon dioxide).

According to the present invention, there is provided the use of 2-ethylhexyl nitrate and one or more organic peroxides in a diesel fuel composition for the purpose of improving fuel economy. In the context of this aspect of the invention, the term “improving” embraces any degree of improvement. The improvement may for instance be 0.1% or more, preferably 0.5% or more, more preferably 1% or more, and especially 2% or more of the fuel economy of an analogous fuel formulation, prior to adding both 2-ethylhexyl nitrate and one or more organic peroxides to it in accordance with the present invention. The improvement in fuel economy may be at most 5% of the fuel economy of an analogous fuel formulation, prior to adding both 2-ethylhexyl nitrate and one or more organic peroxides to it in accordance with the present invention.

In accordance with the present invention, the fuel economy of a fuel composition may be determined in any known manner, for instance using the standard test procedure according to EEC Directive 90/C81/01 using the New European Drive Cycle (NEDC) for a vehicle on a chassis dynamometer or a bench engine. This provides a so-called “measured” fuel consumption number obtained under engine running conditions. Alternatively, the fuel economy performance of a fuel composition may be determined using the “Fuel Economy Test Method” described in the Examples of the present application. In some embodiments, the methods/uses encompass adding 2-EHN and one or more organic peroxides to a fuel composition so as to adjust the fuel economy performance or to achieve or reach a desired target fuel economy value. In the context of the invention, to “reach” a target fuel economy value can also embrace exceeding that number. Thus, the target fuel economy number may be a target minimum fuel economy value.

The concentration of the 2-EHN and the one or more peroxides used may depend on desirable fuel characteristics/properties, such as: the desired combustability of the overall fuel composition; the combustability of the composition prior to incorporation of the additive; the combustability and/or stability of the additive itself; and/or the properties of any solvent in which the additive is used. By way of example, the concentration of the one or more organic peroxides in the fuel composition may be up to 1% w/w and suitably up to 0.5% w/w. Thus, the concentration of the one or more peroxides may be from 0.001% w/w to 1% w/w, from 0.003% w/w to 0.005% w/w, or from 0.005% w/w to 0.5% w/w. In some cases, the concentration of the one or more peroxides is from 0.001% w/w to 1.0 w/w, such as 0.001% w/w, 0.01% w/w, 0.025% w/w, 0.05% w/w, 0.1% w/w, 0.5% w/w or 1.0% w/w based on the total weight of the fuel composition.

With regard to the concentration of 2-EHN, the same concentration ranges may apply to the concentration of 2-EHN as specified above for the concentration ranges of the one or more organic peroxides.

With regard to the combination of 2-EHN and one or more peroxides, the same concentration ranges may apply to the total combination of 2-EHN and one or more peroxides as are given above for the concentration ranges of 2-EHN and for the concentration ranges of one or more peroxides. It will be appreciated that amounts/concentrations may also be expressed as ppm, in which case 1% w/w corresponds to 10,000 ppm w/w.

The remainder of the composition will typically consist of one or more automotive base fuels optionally together with one or more fuel additives, for instance as described in more detail below.

The engine in which the fuel composition of the invention is used may be any appropriate engine. Thus, where the fuel is a diesel, including a biodiesel, fuel composition, the engine is a diesel or compression ignition engine. Likewise, any type of diesel engine may be used, such as a turbo charged diesel engine, provided the same or equivalent engine is used to measure fuel economy with and without the fuel economy increasing components. Generally, the fuel economy improvers of the invention are suitable for use over a wide range of engine working conditions.

An essential component of the fuel compositions herein is one or more organic peroxides. Preferably, the one or more organic peroxides are selected from the group of peroxides represented by formula (I) below:

wherein R₁, R₃, and R₅ are independently selected from the group consisting of hydrogen, C₁-C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ aralkyl and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; R₂, R₄ and R₆ are independently selected from the group consisting of hydrogen, C₂-C₂₀ alkyl, C₃-C₂₀ aryl, C₇-C₂₀ aralkyl, and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; and each of R₁ to R₆ may optionally be substituted with one or more groups selected from hydroxyl, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido.

The cyclic ketone peroxide(s) can be produced as described in WO96/03397. Further details on the preparation methods and other aspects of the cyclic ketone peroxide(s) can be found in WO99/32584.

Suitable ketones for use in the synthesis of cyclic ketone peroxides as used in the invention include, for example, acetone, acetophenone, methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylisoamyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, dimethyl ketone, diethyl ketone, dipropyl ketone, methylethyl ketone, methylisobutyl ketone, methyl isopropyl ketone, methylpropyl ketone, methyl tert-butyl ketone, isobutylheptyl ketone, diisobutyl ketone, 2,4-pentanedione, 2,4-hexanedione, 2,4-heptanedione, 3,5-heptanedione, 3,5-octanedione, 5-methyl-2,4-hexanedione, 2,6-methyl-3,5-heptanedione, 2,4-octanedione, 5,5-dimethyl-2,4-hexanedione, 6-methyl-2,4-heptanedione, 1-phenyl-1,3-propanedione, 1-phenyl-1,3-pentanedione, 1,3-diphenyl-1,3-propanedione, 1-phenyl-2,4-pentanedione, methylbenzylketone, phenylmethyl ketone, phenylethyl ketone, and coupling products thereof. Of course, other ketones having appropriate R groups corresponding to the peroxides of formula (I) can also be used, as well as mixtures of two or more ketones.

Examples of preferred peroxides of formula (I) for use in accordance with the present invention are the cyclic ketone peroxides derived from methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methylpropyl ketone, diethyl ketone, methylethyl ketone, isomers of these ketones, and mixtures thereof. More preferably the peroxides of formula (I) are based on at least one ketone selected from the group consisting of methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methylpropyl ketone, diethyl ketone, methylethyl ketone, and one or more isomers of these ketones, such as methyl-isobutyl ketone and methylisopropyl ketone.

In preferred embodiments herein the cyclic ketone peroxide of formula (I) is selected from the group consisting of cyclic methylethyl ketone peroxide, cyclic methylisobutyl ketone peroxide, and cyclic methylisopropyl ketone peroxide.

In a particularly preferred embodiment herein the cyclic ketone peroxide of formula (I) is cyclic methylethyl ketone peroxide.

A particularly preferred cyclic ketone peroxide for use herein is 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane which is commercially available from Akzo-Nobel under the tradename Trigonox 301. Trigonox 301 is a solution of 41% w of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane in isoparafinic solvent.

In addition to 2-EHN and the one or more peroxides, the fuel composition herein may comprise one or more cetane number enhancers. Cetane number enhancers are known and commercially available, and may also be known (in the context of diesel fuels) as “cetane (number) improvers”, “combustion improvers” and “ignition improvers” etc. as previously described.

Cetane enhancers are often added to diesel fuels, at additive levels (typically 10 to 2000 ppm w/w).

They function to reduce the ignition delay, i.e. the period between the time of injection of the fuel and the start of combustion (ignition).

The cetane number (CN) of a fuel is defined by reference to the ignition properties of standard mixtures of n-hexadecane (cetane, CN=100) and 2,2,4,4,6,8,8-hepta-methylnonane (CN=15). A fuel with a high CN has a short ignition delay. Typically, molecules with high octane numbers, which confer a resistance to spontaneous ignition in gasoline spark ignition engines, have low cetane numbers. The addition of small amounts of cetane enhancers to a diesel fuel may, therefore, result in improved fuel properties based on the shorter ignition delay.

Known cetane number enhancers include, but are not limited to certain organic nitrates other than 2-EHN (e.g. isopropyl nitrate, cyclohexyl nitrate, and methoxyethyl nitrate) and organic peracids and peresters.

In use, the 2-EHN and the one or more peroxides may be pre-dissolved in a suitable solvent, for example an oil such as a mineral oil or Fischer-Tropsch derived hydrocarbon mixture; a fuel component (which again may be either mineral or Fischer-Tropsch derived) compatible with the diesel fuel composition in which the additive is to be used (for example a middle distillate fuel component such as a gas oil or kerosene); a poly alpha olefin; a so-called biofuel such as a fatty acid alkyl ester (FAAE), a Fischer-Tropsch derived biomass-to-liquid synthesis product, a hydrogenated vegetable oil, a waste or algae oil or an alcohol such as ethanol; an aromatic solvent; any other hydrocarbon or organic solvent; or a mixture thereof. Preferred solvents for use in this context are mineral oil based diesel fuel components and solvents, and Fischer-Tropsch derived components such as the “XtL” components referred to below. Biofuel solvents may also be preferred in certain cases. Typically, the 2-EHN and the one or more peroxides will be part of an additive (performance) package additionally containing other additives such as detergents, anti-foaming agents, corrosion inhibitors, dehazers etc. Alternatively, the 2-EHN and the one or more peroxides may be blended directly with the base fuel.

The relative proportions of the 2-EHN, one or more peroxides, fuel components and any other components or additives present in a diesel fuel composition prepared according to the invention may also depend on other desired properties such as density, emissions performance and viscosity.

Diesel Fuel Compositions

In one aspect of the invention, there is provided a diesel fuel composition, which comprises 2-EHN and one or more peroxides of the general formula (I) above, preferably cyclic methylethyl ketone peroxide. It has been found that a combination of 2-EHN and such peroxides, e.g. cyclic methylethyl ketone peroxide, has surprising advantages in terms of providing an improvement in fuel economy performance.

A particularly preferred cyclic ketone peroxide for use in the diesel fuel composition of the present invention is 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane which is commercially available from Akzo-Nobel under the tradename Trigonox 301.

The concentrations of 2-EHN and peroxide of general formula (I), e.g. cyclic methylethyl ketone peroxide, are in the same ranges as given above for the one or more organic peroxides.

A diesel fuel composition prepared in accordance with the present invention may in general be any type of diesel fuel composition suitable for use in a compression ignition (diesel) engine; and it may itself comprise a mixture of diesel fuel components.

Thus, in addition to the 2-EHN and one or more organic, suitably, cyclic peroxides, a diesel fuel composition prepared according to the present invention may comprise one or more diesel fuel components of conventional type. It may, for example, include a major proportion of a diesel base fuel, for instance of the type described below. In this context, a “major proportion” means at least 50% w/w, and typically at least 85% w/w based on the overall composition. More suitably, at least 90% w/w or at least 95% w/w. In some cases at least 98% w/w or at least 99% w/w of the fuel composition consists of the diesel base fuel. Accordingly, in some embodiments, the base fuel may itself comprise a mixture of two or more diesel fuel components of the types described below.

Typical diesel fuel components comprise liquid hydrocarbon middle distillate fuel oils, for instance petroleum derived gas oils. Such base fuel components may be organically or synthetically derived, and are suitably obtained by distillation of a desired range of fractions from a crude oil. They will typically have boiling points within the usual diesel range of 150 to 410° C. or 170 to 370° C., depending on grade and use. They will typically have densities from 0.75 to 0.9 g/cm³, such as from 0.8 to 0.86 g/cm³, at 15° C. (IP 365) and measured cetane numbers (ASTM D613) of from 35 to 80, more preferably from 40 to 75. Their initial boiling points will suitably be in the range 150 to 230° C. and their final boiling points in the range 290 to 400° C. Their kinematic viscosity at 40° C. (ASTM D445) might suitably be from 1.5 to 4.5 centistokes. Such fuels are generally suitable for use in compression ignition (diesel) internal combustion engines, of either the indirect or direct injection type.

An automotive diesel fuel composition which results from carrying out the present invention will also suitably fall within these general specifications. Accordingly, it will generally comply with applicable current standard specification(s) such as for example EN 590 (for Europe) or ASTM D975 (for the USA). By way of example, the fuel composition may have a density from 0.82 to 0.845 g/cm³ at 15° C.; a T₉₅ boiling point (ASTM D86) of 360° C. or less; a cetane number (ASTM D613) of 45 or greater; a kinematic viscosity (ASTM D445) from 2 to 4.5 mm²/s at 40° C.; a sulphur content (ASTM D2622) of 50 mg/kg or less; and/or a polycyclic aromatic hydrocarbons (PAH) content (IP391 (mod)) of less than 11% w/w. Relevant specifications may, however, differ from country to country and from year to year and may depend on the intended use of the fuel composition. In particular, its measured cetane number will preferably be from 45 to 70, to 75 or to 80, more preferably from 50 to 65, or at least greater than 50, greater than 55, greater than 60, or greater than 65.

A petroleum derived gas oil, e.g. obtained from refining and optionally (hydro) processing a crude petroleum source, may be incorporated into a diesel fuel composition. It may be a single gas oil stream obtained from such a refinery process or a blend of several gas oil fractions obtained in the refinery process via different processing routes. Examples of such gas oil fractions are straight run gas oil, vacuum gas oil, gas oil as obtained in a thermal cracking process, light and heavy cycle oils as obtained in a fluid catalytic cracking unit, and gas oil as obtained from a hydrocracker unit. Optionally a petroleum derived gas oil may comprise some petroleum derived kerosene fraction. Such gas oils may be processed in a hydro-desulphurisation (HDS) unit so as to reduce their sulphur content to a level suitable for inclusion in a diesel fuel composition. This also tends to reduce the content of other polar species such as oxygen- or nitrogen-containing species. In some cases, the fuel composition will include one or more cracked products obtained by splitting heavy hydrocarbons.

In some embodiments of the present invention, the base fuel may be or contain another so-called “biodiesel” fuel component, such as a vegetable oil, hydrogenated vegetable oil or vegetable oil derivative (e.g. a fatty acid ester, in particular a fatty acid methyl ester, FAME), or another oxygenate such as an acid, ketone or ester. Such components need not necessarily be bio-derived. Where the fuel composition contains a biodiesel component, the biodiesel component may be present in quantities up to 100%, such as between 1% and 99% w/w, between 2% and 80% w/w, between 2% and 50% w/w, between 3% and 40% w/w, between 4% and 30% w/w, or between 5% and 20% w/w. In one embodiment the biodiesel component may be FAME.

A diesel base fuel may consist of or comprise a Fischer-Tropsch derived diesel fuel component, typically a Fischer-Tropsch derived gas oil. As used herein, the term “Fischer-Tropsch derived” means that a material is, or is obtained from, a synthesis product of a Fischer-Tropsch condensation process. A Fischer-Tropsch derived fuel or fuel component will therefore be a hydrocarbon stream in which a substantial portion, except for added hydrogen, is derived directly or indirectly from a Fischer-Tropsch condensation process.

Fischer-Tropsch fuels may be derived by converting gas, biomass or coal to liquid (XtL), specifically by gas to liquid conversion (GtL), or from biomass to liquid conversion (BtL). Any form of Fischer-Tropsch derived fuel component may be used as a base fuel in accordance with the invention.

The base fuel suitably has a low sulphur content, for example at most 1000 mg/kg (1000 parts per million by weight/ppmw). More suitably it will have a low or ultra low sulphur content, for instance at most 500 mg/kg (500 ppmw), such as no more than 350 mg/kg (350 ppmw), and still more suitably no more than 100 or 50 or 10 or even 5 mg/kg (5 ppmw) of sulphur. It may be a so-called “zero-sulphur” fuel; although in some cases it may be desired that the base fuel is not a sulphur free (“zero sulphur”) fuel. Ideally a fuel composition which results from carrying out the present invention will also have a sulphur content falling within these limits.

Furthermore, a fuel composition prepared according to the present invention, or a base fuel used in such a composition may contain one or more fuel additives, or may be additive-free. If additives are included (e.g. added to the fuel at the refinery), it may contain minor amounts of one or more additives. Selected examples or suitable additives include (but are not limited to): anti-static agents; pipeline drag reducers; flow improvers (e.g. ethylene/vinyl acetate copolymers or acrylate/maleic anhydride copolymers); lubricity enhancing additives (e.g. ester- and acid-based additives); viscosity improving additives or viscosity modifiers (e.g. styrene-based copolymers, zeolites, and high viscosity fuel or oil derivatives); dehazers (e.g. alkoxylated phenol formaldehyde polymers); anti-foaming agents (e.g. polyether-modified polysiloxanes); anti-rust agents (e.g. a propane-1,2-diol semi-ester of tetrapropenyl succinic acid, or polyhydric alcohol esters of a succinic acid derivative); corrosion inhibitors; reodorants; anti-wear additives; antioxidants (e.g. phenolics such as 2,6-di-tert-butylphenol); metal deactivators; combustion improvers; static dissipator additives; antioxidants; and wax anti-settling agents. The composition may for example contain a detergent. Detergent-containing diesel fuel additives are known and commercially available. Such additives may be added to diesel fuels at levels intended to reduce, remove or slow the build up of engine deposits. Examples of detergents suitable for use in diesel fuel additives for the present purpose include polyolefin substituted succinimides or succinamides of polyamines, for instance polyisobutylene succinimides or polyisobutylene amine succinamides, aliphatic amines, Mannich bases or amines and polyolefin (e.g. polyisobutylene) maleic anhydrides. Succinimide dispersant additives are described for example in GB-A-960493, EP-A-0147240, EP-A-0482253, EP-A-0613938, EP-A-0557516 and WO-A-98/42808. Particularly preferred are polyolefin substituted succinimides such as polyisobutylene succinimides.

Other detergents suitable for use in diesel fuel additives for the present purpose include quaternary ammonium salts such as those disclosed in US2012/0102826, US2012/0010112, WO2011/149799 and WO2011/110860.

In some embodiments, it may be advantageous for the fuel composition to contain an anti-foaming agent, more preferably in combination with an anti-rust agent and/or a corrosion inhibitor and/or a lubricity enhancing additive.

Where the composition contains such additives (other than the 2-EHN and one or more organic peroxides described hereinabove), it suitably contains a minor proportion (such as 1% w/w or less, 0.5% w/w or less, 0.2% w/w or less), of the one or more fuel additives, in addition to the 2-EHN and the one or more organic peroxides. Unless otherwise stated, the (active matter) concentration of each such additive component in the fuel composition may be up to 10000 ppmw, such as in the range of 0.1 to 1000 ppmw; and advantageously from 0.1 to 300 ppmw, such as from 0.1 to 150 ppmw.

If desired, one or more additive components, such as those listed above, may be co-mixed (e.g. together with suitable diluent) in an additive concentrate, and the additive concentrate may then be dispersed into a base fuel or fuel composition. In some cases, it may be possible and convenient to incorporate the 2-EHN and/or the one or more organic peroxides into such an additive formulation. Thus, the 2-EHN and/or one or more organic peroxides may be pre-diluted in one or more such fuel components, prior to its incorporation into the final automotive fuel composition. Such a fuel additive mixture may typically contain a detergent, optionally together with other components as described above, and a diesel fuel-compatible diluent, which may be a mineral oil, a solvent such as those sold by Shell companies under the trade mark “SHELLSOL”, a polar solvent such as an ester and, in particular, an alcohol (e.g. hexanol, 2-ethylhexanol, decanol, isotridecanol and alcohol mixtures such as those sold by Shell companies under the trade mark “LINEVOL”, especially LINEVOL 79 alcohol which is a mixture of C₇₋₉ primary alcohols, or a C₁₂₋₁₄ alcohol mixture which is commercially available).

The total content of the additives in the fuel composition may be suitably between 0 and 10000 ppmw and more suitably below 5000 ppmw.

As used herein, amounts (e.g. concentrations, ppmw and % w/w) of components are of active matter, i.e. exclusive of volatile solvents/diluent materials.

An automotive diesel fuel composition prepared according to the present invention will suitably comply with applicable current standard specification(s) such as, for example, EN 590 (for Europe) or ASTM D-975 (for the USA). By way of example, the overall fuel composition may have a density from 820 to 845 kg/m³ at 15° C. (ASTM D-4052 or EN ISO 3675); a T95 boiling point (ASTM D-86 or EN ISO 3405) of 360° C. or less; a measured cetane number (ASTM D-613) of 51 or greater; a VK 40 (ASTM D-445 or EN ISO 3104) from 2 to 4.5 mm²/s; a sulphur content (ASTM D-2622 or EN ISO 20846) of 50 mg/kg or less; and/or a polycyclic aromatic hydrocarbons (PAH) content (IP 391 (mod)) of less than 8% w/w. Relevant specifications may, however, differ from country to country and from year to year, and may depend on the intended use of the fuel composition.

It will be appreciated, however, that a diesel fuel composition prepared according to the present invention may contain fuel components with properties outside of these ranges, since the properties of an overall blend may differ, often significantly, from those of its individual constituents.

Uses and Methods

In accordance with one aspect of the invention, there is provided the use of 2-EHN and one or more organic peroxides for improving the fuel economy performance of a fuel composition. In the context of the present invention, use of 2-EHN and one or more organic peroxides in a fuel composition means incorporating the 2-EHN and/or the one or more organic peroxides into the composition, typically as a blend (i.e. a physical mixture) with one or more fuel components (typically diesel base fuels) and optionally with one or more fuel additives.

The 2-EHN and the one or more organic peroxides are preferably incorporated into the fuel composition before the composition is introduced into an engine which is to be run on the composition. Accordingly, the 2-EHN and the one or more organic peroxides may be dosed directly into (e.g. blended with) one or more components of the fuel composition or the base fuel at the refinery. For instance, they may be pre-diluted in a suitable fuel component, which subsequently forms part of the overall automotive fuel composition. Alternatively, they may be added to a diesel fuel composition downstream of the refinery. For example, they may be added as part of an additive package containing one or more other fuel additives. This can be particularly advantageous because in some circumstances it can be inconvenient or undesirable to modify the fuel composition at the refinery. For example, the blending of base fuel components may not be feasible at all locations, whereas the introduction of fuel additives, at relatively low concentrations, can more readily be achieved at fuel depots or at other filling points such as road tanker, barge or train filling points, dispensers, customer tanks and vehicles.

The 2-EHN and/or one or more organic peroxides may be supplied as a component of a formulation which is suitable for and/or intended for use as a fuel additive, in particular a diesel fuel additive. By way of example, the 2-EHN and/or one or more organic peroxides may be incorporated into an additive formulation or package along with one or more other fuel additives. As described above, the one or more fuel additives may be selected from any useful additive, such as detergents, anti-corrosion additives, esters, poly-alpha olefins, long chain organic acids, components containing amine or amide active centres, and mixtures thereof, as is known to the person of skill in the art.

According to another aspect of the invention, there is provided a process for the preparation of an automotive fuel composition, which process involves blending a diesel base fuel (or base fuel mixture) with 2-EHN and one or more organic peroxides, such as a cyclic methylethyl ketone peroxide. The blending may be carried out for one or more of the purposes described herein.

In some cases the 2-EHN and/or the one or more organic peroxides may not be suitable for pre-mixing with other fuel additives and may, therefore, be dosed directly into the fuel composition from a concentrated (100%) or pre-diluted stock.

It has been found that the combination of 2-EHN and one or more organic peroxides, such as cyclic methylethyl ketone peroxide, can, at relatively low concentrations, improve the fuel economy of a diesel fuel composition by an amount greater than other known cetane enhancers under some engine operating conditions, for example under harsh engine working conditions (e.g. high engine speeds and powers).

While the amount of the 2-EHN and the one or more organic peroxides for use in accordance with the invention may vary depending of fuel type and/or engine working conditions to be used, a further benefit of the invention is that under some engine conditions the amount of 2-EHN and/or the one or more organic peroxides needed to observe the benefit of the invention may be surprisingly low, such as at the level of typical fuel additives.

This in turn can reduce the cost and complexity of the fuel preparation process. For example, it can allow a fuel composition to be altered in order to improve certain properties, by the incorporation of additives downstream of the refinery, rather than by altering the content of the base fuel at its point of initial preparation. The blending of base fuel components may not be feasible at all locations, whereas the introduction of fuel additives, at relatively low concentrations, can more readily be achieved at fuel depots or at other filling points such as road tanker, barge or train filling points, dispensers, customer tanks and vehicles. This in particular may be achievable where the 2-EHN and/or one or more organic peroxides is sufficiently stable to allow it to be transported under suitable conditions without taking unnecessary safety risks. Of course, in some case it may not be appropriate due to safety factors to transport the 2-EHN and/or the one or more organic peroxides.

Moreover, an additive which is to be used at a relatively low concentration can naturally be transported, stored and introduced into a fuel composition more cost effectively than can a fuel component which needs to be used at concentrations of the order of tens of percent by weight.

Another aspect of the invention provides a method of operating an internal combustion engine and/or a vehicle powered by such an engine, which comprises introducing into a combustion chamber of the engine a fuel composition prepared in accordance with the invention. The fuel composition is advantageously introduced for one or more of the purposes described in connection with this invention. Thus, the engine is preferably operated with the fuel composition for the purpose of improving fuel economy during use of the engine and, for example, associated benefits such as reduced engine emissions, etc. The engine is in particular a diesel engine, and may be a turbo charged diesel engine. The diesel engine may be of the direct injection type, for example of the rotary pump, in-line pump, unit pump, electronic unit injector or common rail type, or of the indirect injection type. It may be a heavy or a light duty diesel engine. For example, it may be an electronic unit direct injection (EUDI) engine.

Where relevant to a particular assessment, emission levels may be measured using standard testing procedures such as the European R49, ESC, OICA or ETC (for heavy-duty engines) or ECE+EUDC or MVEG (for light-duty engines) test cycles. Ideally emissions performance is measured on a diesel engine built to comply with the Euro II standard emissions limits (1996) or with the Euro III (2000), IV (2005) or even V (2008) standard limits.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the present invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Thus, features of the uses of the invention are directly applicable to the methods of the invention. Moreover, unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

The invention will now be further illustrated by way of the following non-limiting examples.

EXAMPLES Example 1 Combustion Properties of Fuels Containing 2-EHN and Peroxides

Certain organic peroxide compounds were blended at various levels into a standard low sulphur diesel fuel compliant with EN590 containing 600 mg/kg of 2-EHN. The specification of the base fuel is shown in Table 1 below. The type and concentration of organic peroxide compound in each fuel blend is shown in Table 3 below.

TABLE 1 Density IP365 836.1 kg/m³ Kinematic Viscosity at 40° C. IP71 2.738 mm²/s Initial boiling point IP123 169.8° C. Cold Filter Plugging Point IP309 −16° C. Cloud Point IP219 −3° C. Lubricity (HFRR wear scar ISO 12156 163 μm diameter) Sulphur ISO 20846 6.9 mg/kg Total aromatics IP391 19.8% m/m

The fuel blends to be tested were subjected to ignition testing in a Combustion Research Unit (CRU) obtained from Fueltech Solutions AS/Norway. Fuels were injected into a constant volume combustion chamber preconditioned as set out in Table 2 below.

The Derived Ignition Quality (DIQ) was determined as a function of Ignition Delay (ID) recorded as the time from start of injection (SOI) to the point where the chamber pressure has risen to 0.2 bar above the pressure before SOI, denoted as DIQ^(0.2) (ID^(0.2)). The results of these experiments are shown in Table 3.

TABLE 2 Chamber Injection Pulse Chamber pressure/ pressure/ width/ Condition Temperature/° C. bar bar ms 01 590 75 900 0.9 02 560 50 900 0.9 03 530 30 900 0.9 04 590 65 1600 1.5 05 570 21.4 200 1.5

TABLE 3 Type Concen- of tration of Perox- peroxide DIQ^(0.2) @ condition Fuel ide (mg/kg) 01 02 03 04 05 F1 (Base none n/a 56.7 55.6 58.1 54.6 51.6 fuel including 600 mg/kg 2-EHN) F2 DTBP 100 56.6 55.0 57.9 56.6 51.6 F3 DTBP 300 57.8 56.4 60.2 56.6 52.2 F4 TTTP 100 58.1 56.6 59.0 55.6 52.2 F5 TTTP 300 60.5 59.4 60.8 59.5 53.1 In Table 3, the abbreviations used have the following meanings: DTBP = ditertbutylperoxide (commercially available from Akzo Nobel under the tradename Trigonox B); TTTP = 3,6,9-Triethyl-3,6,9-trimethyl-1,4,7-triperoxonane (commercially available from Akzo Nobel under the tradename Trigonox 301). In simple terms the higher the DIQ^(0.2) value, the better the performance. The results of Table 3 demonstrate both peroxides perform well in conjunction with 2-EHN, but that the better performing peroxide is the cyclic ketone peroxide TTTP.

Example 2 Measuring Ignition Quality on CID 510

The ignition quality of 2-EHN and/or organic peroxide containing fuels was also investigated using the standard test method PAC cetane ID510 (according to ASTMD7668). 2-EHN and/or the organic peroxide TTTP were blended into market diesel fuel compliant to EN590. Selected properties of the base fuel are shown in Table 4 below. Table 5 shows the concentration of 2-EHN and TTTP used in each fuel blend tested. Table 5 also shows the Derived Cetane Number (DCN) of each of the fuel blends tested in this Example.

FIG. 1 shows the Derived Cetane Number (DCN) of each of the fuel blends tested in Example 2.

TABLE 4 Density DIN EN ISO 12185 843.1 kg/m³ Initial boiling point DIN EN ISO 3405 174.4° C. Cold Filter Plugging DIN EN 116 −16° C. Point Cloud Point DIN EN 23015 −5° C. Sulphur ISO 20846 <10 mg/kg

TABLE 5 2-EHN (mg/kg) TTTP (mg/kg) DCN 0 0 54.04 300 0 55.95 600 0 56.89 900 0 57.59 1200 0 59.05 1500 0 59.45 1800 0 59.98 2100 0 60.99 2400 0 61.37 0 0 54.04 0 300 56.13 0 600 56.03 0 900 57.38 0 1200 58.29 0 1500 59.12 0 1800 59.53 0 2100 59.95 0 2400 60.10 0 300 56.13 600 0 57.23 600 300 59.03 600 600 59.10 600 900 58.57 600 1200 59.04 600 1500 59.61 600 1800 60.18

Example 3 Fuel Economy Test Method: Measurement of Fuel Consumption Benefits

Fuel consumption was measured using a Renault Megane (1.5 dCi common rail engine, max power output 78 kw, DPF, EURO4 emissions standard, manufacturing year 2009) run at constant speed of 50 km/h on a chassis dynamometer (CD) applying road load conditions with automated driving. The test cell was preconditioned to 23° C. FC consumption was measured gravimetrically using a corriolis device (Siemens) over a period of 30 minutes. Test and reference fuel were each repeated eight times in an A-B-A-B . . . and so on test design. Fuel was taken from individual 25 L drums and all lines were flushed with the fuel to be tested test before restarting the measurement. The overall fuel consumption of a test fuel was compared with overall fuel consumption of a reference fuel to obtain a fuel economy benefit.

Fuels were blended by dissolving either 2-EHN and/or organic peroxide into market typical AGO (Automotive Gas Oil) from the German market complying with DIN EN590. Table 6 below shows the properties of the AGO base fuel.

TABLE 6 Density DIN EN ISO 12185 839.1 kg/m³ Initial boiling point DIN EN ISO 3405 169.7° C. Kinematic Viscosity DIN EN ISO3104 2.567 mm²/s Sulphur DIN EN ISO 20884 7 mg/kg Flash point DIN EN ISO 2719 63.0° C. Cetane Number DIN EN ISO 5165 50.7

The reference fuel was the base AGO fuel with the addition of 600 mg/kg 2-EHN. The test fuel was the reference fuel with the addition of 600 mg/kg (on an active matter basis) of Trigonox 301.

Table 7 below shows the fuel consumption of the fuels tested together with the % improvement in fuel economy benefit of the test fuel compared with the reference fuel.

TABLE 7 FC of Reference Fuel FC of Test Fuel Repeat (L per 100 km) (L per 100 km) FE benefit/% 1 2.788 2.771 0.62 2 2.783 2.767 0.57 3 2.780 2.761 0.69 4 2.811 2.802 0.31 5 2.787 2.771 0.58 6 2.776 2.770 0.24 7 2.795 2.773 0.78 8 2.783 2.763 0.71 average 2.788 2.772 0.56

DISCUSSION

The results shown in Table 7 demonstrate an improvement in fuel economy for the test fuel (containing a combination of 2-EHN and Trigonox 301) compared to the reference fuel (containing 2-EHN only). 

We claim:
 1. A diesel fuel composition comprising a diesel base fuel, 2-ethylhexylnitrate and one or more peroxides selected from the group of peroxides represented by the general formula (I) below:

wherein R₁, R₃, and R₅ are independently selected from the group consisting of hydrogen, C₁-C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ aralkyl and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; R₂, R₄ and R₆ are independently selected from the group consisting of hydrogen, C₂-C₂₀ alkyl, C₃-C₂₀ aryl, C₇-C₂₀ aralkyl, and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; and each of R₁ to R₆ may optionally be substituted with one or more groups selected from hydroxyl, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido.
 2. The diesel fuel composition of claim 1 wherein the amount of the one or more peroxides is in the range of from 0.001% w/w to 1% w/w, based on the weight of the total diesel fuel composition.
 3. The diesel fuel composition of claim 1 wherein the amount of 2-ethylhexyl nitrate is in the range of from 0.001% w/w to 1% w/w, based on the weight of the total diesel fuel composition.
 4. The diesel fuel composition of claim 1 wherein at least one of the peroxides in the fuel composition is derived from one or more ketones selected from the group consisting of acetone, methyl-n-amyl ketone, ethyl butyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methylpropyl ketone, diethyl ketone, methylethyl ketone, isomers of these ketones, and mixtures thereof.
 5. The diesel fuel composition of claim 1 wherein the cyclic ketone peroxide of general formula (I) is selected from the group consisting of cyclic methylethyl ketone peroxide, cyclic methylisobutyl ketone peroxide, and cyclic methylisopropyl ketone peroxide.
 6. The diesel fuel composition of claim 1 comprising 2-ethylhexylnitrate and cyclic methylethyl ketone peroxide.
 7. The diesel fuel composition of claim 6 wherein the cyclic methylethyl ketone peroxide is 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.
 8. The diesel fuel composition of claim 1 further comprising one or more fuel additives.
 9. A method of operating an internal combustion engine and/or a vehicle powered by such an engine comprising introducing into a combustion chamber of the engine the diesel fuel composition of claim 1 and operating the internal combustion engine and/or the vehicle powered by such an engine.
 10. A method of improving the fuel economy performance of an internal combustion engine comprising introducing into a combustion chamber of the internal combustion engine a diesel fuel composition of claim
 1. 